1. Field of the Invention
The invention relates to an amplifier comprising: a current mirror having an mirror input terminal, a mirror output terminal, a mirror control terminal, and a common terminal; a differential transistor pair comprising first and second transistors having respective control electrodes connected to receive an input signal, and having respective output electrodes coupled to the mirror input terminal and the mirror output terminal; a differential amplifier having an non-inverting input coupled to the mirror input terminal, an inverting input to the mirror output terminal and an output coupled to the mirror control terminal; and a capacitor.
2. Description of the Related Art
Such an amplifier is known from U.S. Pat. No. 4,068,184. High gain in amplifiers is generally achieved by cascading a number of gain stages. The number of cascaded stages is limited by the need for frequency compensation to enable stable feedback. Particularly CMOS processes yield relatively low gain values. The gain per stage is then usually increased by cascading techniques. Unfortunately, cascaded circuits involve stacking of transistor voltage drops. This limits the use of cascading for low supply-voltage circuits. Another gain-enhancement technique is based on bootstrapping. In the known amplifier this bootstrapping technique would imply omitting the differential amplifier, interconnecting the mirror control terminal and the mirror input terminal, and adding a current source in series with the common terminal of the current mirror and a voltage-follower transistor which buffers the voltage at the mirror output terminal to the common terminal of the current mirror, thereby forcing nearly equal signal voltages at the mirror input terminal and the mirror output terminal. However, the current source in series with the common terminal of the current mirror causes an additional transistor voltage drop.